Influenza is a form of acute inflammation starting from virus growth in the throat or the upper respiratory mucous membrane caused by infection with influenza viruses (type A, type B, or type C). In addition to inflammation in the respiratory tract, constitutional symptoms, such as high fever, feebleness, headache, muscle ache, or arthralgia, develop. Healthy adults recover from such acute inflammation within approximately a week. People with an underlying disease, such as chronic lung disease, renal disease, heart disease, or diabetes, babies and toddlers, and elderly adults are high risk groups that are regarded as being at high risk of developing complications with pneumonia or other diseases (Hiroshi Ochiai, Yakkyoku (Pharmacy), vol. 44, 1231-1237, 1993; Non-Patent Document 1).
In recent years, vaccines become known as influenza prevention measures at the social level, and the influenza vaccination coverage rate is increasing. Since the antigenicity of the influenza virus is likely to vary, effects of vaccines are not stable, and the initial effects cannot be always expected.
In addition to rapid diagnostic techniques, therapeutic agents are remarkably developed, and oseltamivir phosphate and the like are stocked in preparation for the flu season. However, the appearance of resistant viruses, side effects resulting from ingestion, and the like have been reported, and therapeutic drugs cannot be regarded as being problem-free. The present applicant considered that searching for of substances having anti-influenza virus activity from among naturally-occurring substances, which are safe and easily obtained, or extracts thereof would be significant in view of the dangerous nature of influenza. Thus, the present applicant has heretofore focused on mushrooms, which have been artificially cultivated in large quantities as food materials, and in particular, Grifola frondosa mushrooms, which have been reported to have immunostimulatory activity.
A variety of effects of Grifola frondosa extracts have been known because of development efforts made by the present applicant and others. For example, effects of ameliorating AIDS are reported in JP Patent Publication (kokai) No. H7-69913 (A) (1995) (Patent Document 1), anti-tumor effects are reported in JP Patent Publication (kokai) No. H9-238697 (A) (1997) (JP Patent No. 2859843; Patent Document 2), activity of eliminating active oxygen is reported in JP Patent Publication (kokai) No. 2000-119650 (A) (JP Patent No. 3260329; Patent Document 3), and activity of inducing NO production is reported in JP Patent Publication (kokai) No. 2001-172194 (A) (Patent Document 4).
The present inventors have conducted concentrated studies regarding the ingredients of Grifola frondosa. As a result, they discovered that a hot-water extract of Grifola frondosa had anti-influenza virus activity, and they filed a patent application (i.e., JP Patent Publication (kokai) No. 2005-145934 (A) (Patent Document 5). A discovery of bio-defense activity, such as anti-influenza virus activity, in extracted fractions of Grifola frondosa mushrooms, which are safe, mass-produced as food materials, is very significant.
It is demonstrated that the defense mechanism against infection; i.e., the immune system, involves phagocytosis via non-specific recognition (i.e., natural immunity or a non-specific defense mechanism) caused by macrophages (hereafter abbreviated as “Mφ”) and the like upon infection with viruses or the like. It is also demonstrated that cytokines are released or antigens are presented on the cell surface, and helper T cells receive signals to activate a more sophisticated defense mechanism, when the viruses cannot be fully treated (i.e., acquired immunity or a specific defense mechanism). When the acquired immune system is activated, further, T cells, NK cells, and the like may be activated (i.e., cell-mediated immunity). Alternatively, B cells may be activated (i.e., humoral immunity). Based on the research conducted in the past, nature of a Grifola frondosa ingredient exhibiting anti-tumor activity has been demonstrated to be a β-D-glucan-type polysaccharide (i.e., a sugar component of a sugar-protein complex) having a special chemical structure (a β-1,6 main chain and β-1,3 side chains) (Chem. Pharm. Bull., 35 (3), 1162-1168, 1987, Non-Patent Document 2). Thereafter, Grifola frondosa ingredients having other chemical structures that exhibit excellent anti-tumor effects have not yet been discovered. Such action mechanism has been found to involve activation of the cell-mediated immune system that starts from activation of macrophages (Biol. Pharm. Bull., 25 (12), 1647-1650, 2002, Non-Patent Document 3).
In the past, the present applicant invented a sugar-protein complex (Patent Document 2), which was obtained by purifying a hot-water extract of Grifola frondosa mushrooms via alcohol treatment, and demonstrated that such sugar-protein complex was an anti-tumor substance having excellent immunostimulatory activity. The present inventors deduced that extracts of Grifola frondosa mushrooms having immunostimulatory activities starting from Mφ activation would provide useful actions in protection against virus infection. As a result of the research, they discovered that TNF-α would be released upon Mφ activation and that TNF-α would function as a virus proliferative inhibitory factor in cells infected with influenza viruses (Patent Document 5). This action takes place at the activation stage of the natural immune system, and drug resistance would not be caused in principle, unlike the action mechanism caused by vaccines. Thus, such action is considered to be significant immunostimulatory activity caused by a food component.
When excellent anti-tumor activity was first discovered in a sugar-protein complex (a sugar component is composed of β-D-glucan) contained in Grifola frondosa, giant macromolecules having molecular weights of about 1,000,000 or greater had been the subjects of focus. In general, substances having greater molecular weights are more likely to experience cleavage of molecular bonds during the process of purification, and purification of such substances without damage is likely to be difficult. Also, the amount of contaminants contained in an extract from naturally-occurring substances tends to increase in substances having lower molecular weights.    Patent Document 1: JP Patent Publication (kokai) No. H7-69913 (A) (1995)    Patent Document 2: JP Patent Publication (kokai) No. H9-238697 (A) (1997)    Patent Document 3: JP Patent Publication (kokai) No. 2000-119650 (A)    Patent Document 4: JP Patent Publication (kokai) No. 2001-172194 (A)    Patent Document 5: JP Patent Publication (kokai) No. 2005-145934 (A)    Non-Patent Document 1: Hiroshi Ochiai, Yakkyoku (Pharmacy), vol. 44, 1231-1237, 1993    Non-Patent Document 2: Chem. Pharm. Bull., 35 (3), 1162-1168, 1987    Non-Patent Document 3: Biol. Pharm. Bull., 25 (12), 1647-1650, 2002